1. Field of the Invention
The present invention relates to an electromagnetic relay and, particularly, to an electromagnetic relay for forward reverse control, such as a motor and a solenoid.
2. Description of the Related Art
FIG. 12 is a block diagram showing a forward reverse control circuit. A forward reverse control circuit 1 is provided with two electromagnetic relays 2 and 3. An A-terminal 2a of one of the electromagnetic relays 2 and 3 (hereinafter referred to as first electromagnetic relay 2) is connected to a plus electric source (hereinafter referred to as +E); a B-terminal 2b of the first electromagnetic relay 2 is connected to a ground potential (hereinafter referred to as GND); and a C-terminal 2c of the first electromagnetic relay 2 is connected to one of terminals (terminal 4a) of a load 4 such as a motor and solenoid. An A-terminal 3a of the other electromagnetic relay 3 (hereinafter referred to as second electromagnetic relay 3) is connected to the +E; a B-terminal 3b of the second electromagnetic relay 3 is connected to the GND; and a C-terminal 3c of the first electromagnetic relay 2 is connected to the other terminal 4b of the load 4. As used herein, the alphabet A added to each of the terminals means that the terminal is connected to an A-contact (normal open contact); the alphabet B means that the terminal is connected to a B-contact (normal close contact); and the alphabet C means that the terminal is connected to a C-contact (COM contact).
In such forward reverse control circuit 1, since the terminal 4a of the load 4 is connected to the GND via a contact 2e of the first electromagnetic relay 2 and the terminal 4b is connected to the GND via a contact 3e of the second electromagnetic relay 3 in a normal state (when the first and the second electromagnetic relays 2 and 3 are in a non-excitation state), the load 4 does not operate in the normal state.
When a control voltage is applied to a coil terminal 2d of the first electromagnetic relay 2, a coil 2f of the first electromagnetic relay 2 is excited to change the position of the contact 2e, so that the terminal 4a of the load 4 is connected to the +E via the contact 2e of the first electromagnetic relay 2. In such state, the second electromagnetic relay 3 is turned off, and the terminal 4b of the load 4 is connected to the GND via the contact 3e of the second electromagnetic relay 3, so that a current flows to the load 4 in a direction (see an arrow A) of “+E→contact 2e of first electromagnetic relay 2→terminal 4a of load 4→terminal 4b of load 4→contact 3e of second electromagnetic relay 3→GND”.
When a control voltage is applied to a coil terminal 3d of the second electromagnetic relay 3, a coil 3f of the second electromagnetic relay 3 is excited to change the position of the contact 3e, so that the terminal 4b of the load 4 is connected to the +E via the contact 3e of the second electromagnetic relay 3. In such state, the first electromagnetic relay 2 is turned off, and the terminal 4a of the load 4 is connected to the GND via the contact 2e of the first electromagnetic relay 2, so that a current flows to the load 4 in a reverse direction (see an arrow B) of “+E→contact 3e of second electromagnetic relay 3→terminal 4b of load 4→terminal 4a of load 4→contact 2e of first electromagnetic relay 2→GND”.
As described above, since it is possible to change the direction of driving current applied to the load 4 such as a motor and a solenoid by the use of the forward reverse control circuit 1 of FIG. 12, it is possible to change a rotation direction of the motor or a driving direction of the solenoid.
By the way, since the forward reverse control circuit 1 of FIG. 12 requires two electromagnetic relays, the forward reverse control circuit 1 undesirably needs extra effort and a relatively large mounting space when it is integrated into an appliance.
FIG. 13 is a conceptual diagram showing a conventional technology which resolves the above drawbacks (see, for example, Patent Literature 1). Referring to FIG. 13, an electromagnetic relay 5 is provided with a rectangular base 6 having a length La, and a pair of electromagnets 7 and 8 disposed parallelly to each other on the base 6, armatures 9 and 10 disposed on the electromagnets 7 and 8, a pair of insulators 11 and 12 disposed on side faces of the armatures 9 and 10, a pair of moving contact springs 13 and 14 sandwiched between the insulators 11 and 12, and a pair of fixed contact terminal plates 15 and 16 disposed at swinging ends of the moving contact springs 13 and 14 and can be handled as one unit.
Each of the pair of moving contact springs 13 and 14 is an L-shaped flat plate spring, and the moving contact spring 13 is disposed on the moving contact spring 14. Therefore, when the base 6 is viewed from above, the moving contact spring 14 cannot be seen since it is hidden under the moving contact spring 13.
A terminal 13a for connecting a load 17 is formed on a fixed end of the moving contact spring 13, and a terminal 14a for connecting a load 17 is formed on a fixed end of the moving contact spring 14. Moving contacts 13b and 13c are attached to opposite sides of the swinging end of the moving contact spring 13, and moving contacts 14b and 14c are attached to opposite sides of the swinging end of the moving contact spring 14.
The fixed contact terminal plate 15 is provided with a fixed terminal 15a for connecting to the +E and the GND, and the fixed contact terminal plate 16 is provided with a fixed terminal 16a for connecting to the +E and the GND. Fixed contacts 15b, 15c, 16b, and 16c are attached to the fixed contact terminal plates 15 and 16 at predetermined positions. The fixed contacts 15b, 15c, 16b, and 16c contact the moving contacts 13b, 13c, 14b, and 14c in predetermined combinations when the electromagnets 7 and 8 are excited.
The predetermined combinations are (1) the moving contact 13b and the fixed contact 15b, (2) the moving contact 13c and the fixed contact 16c, (3) the moving contact 14b and the fixed contact 16b, and (4) the moving contact 14c and the fixed contact 15c. 
With such constitution, when the electromagnets 7 and 8 are not excited, the combinations of (2) the moving contact 13c and the fixed contact 16c and (3) the moving contact 14b and the fixed contact 16b are employed so that the GND is supplied to both ends of the load 17. When the electromagnet 7 on the left hand side in FIG. 13 is excited in this state, the armature 9 is operated so that the insulator 11 attached to the armature 9 moves to the right. Accordingly, the moving contact spring 13 is pressed by the insulator 11 to move to the right, thereby achieving the combination (1) the moving contact 13b and the fixed contact 15b, so that a current flows in the order of the +E, the terminal 15a, the fixed contact 15b, the moving contact 13b, the moving contact spring 13, the terminal 13a, the load 17, the terminal 14a, the moving contact spring 14, the moving contact 14b, the fixed contact 16b, the terminal 16a, and the GND.
When the electromagnet 8 on the right hand side in FIG. 13 is excited, the armature 10 is operated so that the insulator 12 attached to the armature 10 moves to the left. Accordingly, the moving contact spring 14 is pressed by the insulator 12 to move to the left, thereby achieving the combination (4) the moving contact 14c and the fixed contact 15c, so that a current flows in the reverse order of the +E, the terminal 15a, the fixed contact 15c, the moving contact 14c, the moving contact spring 14, the terminal 14a, the load 17, the terminal 13a, the moving contact spring 13, the moving contact 13c, the fixed contact 16c, the terminal 16a, and the GND.
[Patent Literature 1] Japanese Patent No. 2890581